(20e) Counterintuitive Effect of Fluid Viscosity on Enhancing Cell Motility Via Dynamic Load Response of Actin Network

It is well known that cancer cells respond to physical stimuli, such as stiffness, fluid shear stress and hydraulic pressure. The viscosity of the interstitial fluid is a key physical cue that varies under both physiological and pathological conditions. However, its impact on cancer biology and the mechanism by which cells sense and respond to changes in extracellular viscosity is unknown. Till date, most in vitro cell functional assays, including motility, are performed in medium with a viscosity close to that of water (0.7 cP at 37^oC). However, the viscosity of the interstitial fluid varies up to 3.5 cP, and can be further increased by the presence of macromolecules, such as mucins, secreted by tumor cells. Elevated degradation of extracellular matrix (ECM) at tumor sites also exacerbates macromolecular crowding, which can further increase the viscosity of the interstitial fluid. To investigate this, we employed an interdisciplinary approach integrating sophisticated microfluidic and molecular biology techniques, super resolution imaging and combined mathematical modeling with in vivo zebrafish and chick embryo models. We demonstrate that elevated viscosity counterintuitively increases the motility of breast cancer cells on two-dimensional (2D) surfaces, in confinement (Fig. 1a), and cell dissemination from 3D tumor spheroids. Augmented cell motility was also observed with other cancerous (human osteosarcoma, glioblastoma) and non-cancerous (human aortic smooth muscle cells, fibroblasts) cells under elevated fluid viscosity. Increased mechanical loading imposed on the cell leading edge by elevated viscosity induces an Actin Related Protein 2/3 (Arp2/3) complex-dependent dense actin network (Fig. 1b) and promotes a mesenchymal cell phenotype which leads to faster cell motility. Moreover, breast cancer cells exposed to elevated viscosity exhibit increased migration in zebrafish (Fig. 1c) and increased extravasation in chicken embryo. This presentation will also discuss the role of Osmotic Engine Model in regulating cancer cell migration at physiologically relevant elevated viscosities. Cumulatively, we exhibit that extracellular viscosity is a physical cue that can regulate key (patho)physiological processes like cell migration and cancer metastasis. Our research will also reveal possibilities of investigating if extracellular viscosity affects other physiologically-relevant cellular processes like morphogenesis.